CN101302435A - A method for improving delayed coking process - Google Patents

Abstract

The invention provides a method for improving the delayed coking process. Coking raw material residual oil enters the coke tower after being heated by a heating furnace, and the generated coke is coalesced in the coke tower, and the oil and gas fluid products are separated through the coking fractionation tower to obtain gas and naphtha. , Light diesel oil, heavy diesel oil, light wax oil, heavy wax oil. By adjusting the source, distillation range and circulation volume of the recycle stream, using light diesel oil, heavy diesel oil, light wax oil or heavy wax oil as the recycle stream, the coke induction period of the mixture can be extended, and the coke formation of the coking raw material residue can be changed. Kinetics, so that the coke-forming reaction is more thoroughly delayed to the coke tower, so as to achieve the purpose of prolonging the start-up period of the heating furnace tube. According to the source of the selected recycle stream, the distillation range, and the degree of extension of the coke induction period determined by the circulation volume, the start-up period of the coking furnace can generally be extended by 3 to 18 months.

Description

A method for improving delayed coking process

technical field

The invention belongs to the technical field of chemical engineering, and relates to a delayed coking process improvement method. Specifically, a distillate oil derived from petroleum and coal tar is circulated to prolong the coking induction period of the coking raw material residue to make the coking reaction It is fully delayed to the coke tower to effectively prevent coking in the heating furnace tube, thereby prolonging the start-up period of the coking heating furnace tube.

Background technique

Delayed coking is a decarbonization process that can process residual oil raw materials from a wide range of sources to obtain high value-added light oil products. Since the coking process does not use catalysts, there is no restriction on the residual carbon value of raw materials, metal content, etc.; the investment and operating costs of the delayed coking process are low, and it has generally become residual oil (especially low-quality residue with high residual carbon and high metal content) Oil) is the preferred processing option. The raw material residual oil is gradually heated to 485°C-505°C through the heating furnace tube, and then enters the coke tower through the oil transfer line, where coking and decarburization reactions occur in the coke tower, and the oil and gas products enter the coking fractionation tower to be separated to obtain light oil products, while the coke is Coalescing in the coke drum; the main coking reactions have been "delayed" by the furnace tubes into the coke drum. For different raw material residues and operating conditions, the delay effect is very different, and the delay effect is not directly positively related to the carbon residue value of the raw material residue. For residual oil raw materials with low residual carbon value, if the concentration of free radicals generated in the heating furnace tube is high, these free radicals will quickly dehydrogenate the few asphaltene molecules and quickly form coke, which is manifested as biogenesis. The coke induction period is short, the heating furnace tube is easy to block, and the start-up period is short. In order to prevent the clogging of heating furnace tubes in industry, water steam injection or large circulation ratio measures are often adopted to reduce the residence time of residual oil raw materials in heating furnace tubes and prevent coke deposition and agglomeration, but these measures cause energy consumption of the process system Increase, and even induce the production of projectile coke, bringing production danger. Patent CN1286947C divides a coking cycle into three stages. From one stage to the next stage, it is necessary to adjust the temperature of the heating furnace and switch different raw material oil products. Such frequent adjustments are difficult to achieve stable operation for large coking units. Therefore, how to prevent the coking reaction of coking raw materials in the heating furnace tube from the source, and effectively "delay" the coking reaction in the process to the coke tower, thereby fundamentally inhibiting the coking and clogging of the heating furnace tube and prolonging the start-up period, this is A subject of universal practical value.

Contents of the invention

The object of the present invention is to provide an improved delayed coking process which can make the coking heating furnace operate for a long period.

The object of the present invention is achieved in the following way: firstly measure the thermal reaction coke induction period t ₀ of the residual oil raw material by putting the residual oil raw material into a pressure reactor with a pressure of 1-8 MPa and heating it to 300°C-500°C , keep t _i min at this temperature, after that the reactor temperature is down to normal temperature, disassemble the reactor and dilute the reaction product therein with toluene, filter and extract, the productive rate of toluene insoluble matter (TI) can be obtained; when the TI When the yield is equal to 0.1wt%, the corresponding reaction time t _i of the raw material residue is the thermal reaction coke induction period t ₀ . Then, mix the residual oil raw material with a certain narrow distillate oil, the mixing ratio by weight is 1:0.01～1:5, and measure the thermal reaction coke induction period t ₁ of the residual oil raw material under the mixing condition. The measuring method is Put a certain amount of mixed raw materials into a pressure reactor and heat it to a temperature of 300°C to 500°C, keep it at this temperature for t _i min, then lower the temperature of the reactor to normal temperature, disassemble the reactor and dilute the reaction product therein with toluene, After filtration and extraction, the TI yield based on the residual oil in the mixed raw material can be obtained; when the TI yield is equal to 0.1wt%, the corresponding reaction time t _i of the raw material residual oil is the thermal reaction coke induction period t ₁ . If t ₁ ≤ _{t 0} , then change the quantity and type of narrow distillate oil used for mixing, and re-measure the thermal reaction induction period of residual oil raw material under mixing conditions until t ₁ >t ₀ , the narrow distillate oil and its mixture at this time The amount is called the circulating flow and the circulating amount. Next, feed the residual oil raw material into the delayed coking unit with a metering pump, and at the same time connect an oil inlet pipeline and a metering pump in front of the heating furnace tube, so as to drive the recycle stream into the delayed coker according to the circulation amount, so that the recycle stream and slag Oil ingredients are mixed thoroughly. Finally, driven by pipeline pressure and low injection steam, the mixture is heated to a delayed coking temperature of 485°C to 505°C through a heating furnace gradient, and then enters the coke tower through the oil transfer line, where full coking and decarburization occurs Reaction, the oil and gas products enter the coking fractionation tower to be separated to obtain light oil products, while the coke is coalesced in the coke tower. According to the source of the selected recycle stream, the distillation range, and the degree of extension of the coke induction period (that is, the degree of difference between t ₁ and t ₀ ), the start-up period of the coking furnace can generally be extended by 3 to 18 months.

The above-mentioned residual oil raw material is the residual oil after distilling gasoline and diesel fractions or even vacuum distillate oil, or the carbon-rich residue obtained by solvent deasphalting process or the residual oil obtained from the secondary reaction, and it can also be heavy crude oil or Super heavy crude oil or coal tar can also be a mixture of two or more of the above raw materials.

The recycle stream as described above is a mixture of one or several narrow cuts, wherein the narrow cuts are light diesel oil, heavy diesel oil, light wax oil or heavy wax oil from coking liquid products, or from hydrogenated oil, straight Distillate petroleum fractions, reformate oils, catalytic cracking clear oils, ethylene tars or coal tars.

The recycle stream as described above may contain a certain amount of an active component that promotes the release of hydrogen atoms, the active component being a partially hydrogenated aromatic hydrocarbon having a chemical structure similar to that of tetralin.

The thorough mixing of the recycle stream and the residue feedstock as described above can be accomplished with the aid of a static mixer. The coke induction period mentioned above refers to the time required for the residual oil raw material to start to form coke after a certain temperature rise program, and the unit is generally expressed in minutes.

The circulation amount of the above-mentioned recycle stream accounts for 1wt%-100wt% of the residual oil raw material, and the optimum recycle amount is 5wt%-50wt%.

The amount of steam injected as mentioned above is 0.5wt%-3.0wt% of the residual oil.

Because the delayed coking heating furnace provides all the energy required for the reaction of the residue raw material, and most of the reaction is delayed to the coke tower, which provides the possibility to ensure the continuous progress of the reaction. However, the efficiency of the delayed reaction depends on the length of the coke induction period of the thermal reaction of the residual oil raw material. If the coke induction period is too short, coke formation and accumulation will occur when the temperature of the residual oil raw material is increased in the heating furnace tube. In the end, the heating furnace tube was blocked and was forced to stop working. If the coke induction period is longer, it will be difficult for the residual oil raw material to generate coke when the temperature is raised in the heating furnace tube, so the operating period of the heating furnace tube is longer. The formation mechanism of coke is the condensation reaction of asphaltene free radicals, and to inhibit the condensation reaction of asphaltene free radicals requires a comprehensive reduction of the concentration of asphaltene free radicals. On the premise of ensuring that asphaltene does not precipitate locally, there are two ways: Asphaltene free radicals are quenched by chemical hydrogen donation of hydrogen donors, or the concentration of asphaltene free radicals is reduced by adding solvents through physical dilution. If a diluent solvent is selected, which has a strong hydrogen supply effect under heated conditions, but does not cause physical coagulation of the residual oil raw material, then this solvent is used as a circulating stream to fully mix with the residual oil raw material according to a certain circulation amount and heating to measure the coke induction period of the residual oil raw material, which is obviously longer than that of the residual oil raw material when it is heated alone. The extension of the coke induction period is to improve the coke formation kinetics of the residual oil raw material, so that the coking reaction that occurs when the temperature rises in the delayed coking heating furnace tube can be effectively "delayed" to the coke tower, and the heating furnace tube does not regenerate coke, so its operation period can be extended, and the degree of extension depends on the degree of extension of the coke induction period of the residual oil raw material by the recycle stream.

Detailed ways

The present invention is further described below in conjunction with embodiment, but does not limit the present invention thereby. The raw materials used in Examples and Comparative Examples are one or more of vacuum residue, coker light gas oil narrow cut, coked heavy diesel oil narrow cut, coker light diesel narrow cut; the test used in Examples and Comparative Examples The device is a thermal reaction induction period test device and a pilot-scale delayed coking device. The feed rate of the coking device is 0.5kg·h ^-1 ~ 2.0kg·h ^-1 , the outlet temperature of the heating furnace is 503°C, and the pressure at the top of the coke tower is 0.20 MPa (gauge pressure).

Embodiment: first transfer 20wt% narrow fraction of coking light wax oil into the raw material of coking residue (see Table 1 for properties), mix evenly, take 500g of the mixture and place it in an autoclave, and measure the residue under the condition of heating at 400°C The coke induction period of raw materials was 108 minutes (as shown in Table 2). Then use a metering pump to inject the mixture into the heating furnace tube of the coking device at a uniform speed (the weight during drying has been weighed in advance) and heat it up. The outlet temperature rises to 503°C and enters the coke tower for a thorough coking reaction. The solid coke coalesces. In the coke tower, oil and gas products overflow through the large oil and gas pipeline of the coke tower and enter the fractionation tower for separation. After continuous oil feeding through the heating furnace tube for 24 hours, stop feeding, improve the toluene solvent, and adjust the temperature in the heating furnace tube to 100°C at the same time, and the toluene lotion flows out from the bypass at the outlet of the heating furnace tube until the toluene eluate is colorless. Then use hot high-purity nitrogen to purge the heating furnace tube to carry out all the residual toluene in the tube. The dried heating furnace tube was disassembled and weighed with an electronic balance. The weight gain of the heating furnace tube after the coking reaction is listed in Table 3, which is 2.38g.

Comparative example: In order to compare with the examples, the coke induction period (Table 2) of the above-mentioned coking residual oil raw material was measured, and then the residual oil raw material was injected into the heating furnace tube of the coking device at a uniform speed with a metering pump and heated up. Other operations were the same as Similar to the examples, the increased weight of the obtained heating furnace tube after the coking reaction is listed in Table 3, which is 18.67g.

Table 1 Properties of Coking Residue Raw Materials

nature Residue raw material nature Residue raw material Density (20°C)/kg·m ^-3 carbon residue/wt% viscosity (100°C)/mm ² ·s ^-1 ash/wt% freezing point/°C molecular weight (VPO) four-component composition/wt% saturated aromatics Colloidal n-heptane asphaltenes 1003.520.045500.09546115015.526.252.85.5 Elemental Analysis Carbon/wt% Hydrogen/wt% H/C (atomic ratio) Nitrogen/wt% Sulfur/wt% Metal Content/μg·g ^-1 Nickel Vanadium Iron Calcium 87.0811.261.540.920.37160.32.3123.197.3

Table 2 Heated coke induction period of coking residue raw materials/min

Example comparative example 108 75

Table 3 Weight gain of coking heating furnace tubes before and after the test/g

Example comparative example 2.38 18.67

From the comparison of the above examples and comparative examples, it can be seen that by improving the coking kinetics of the coking residual oil raw material, the coking reaction can be effectively delayed to the coke tower, thereby achieving the goal of suppressing coking in the heating furnace tube and prolonging the start-up period of the heating furnace tube. Purpose.

The invention has the advantage that the start-up period of the heating furnace tube is significantly extended, generally up to 3 to 18 months, and the increased cost is very limited because only the pipeline process needs to be adjusted, so the economic and social benefits are remarkable.

Claims (5)

1. an improved method of delay coking process is characterized in that comprising the steps:

(1) thermal response green coke t inductive phase of mensuration residual oil raw material ₀: residual oil raw material is packed in the pressure reactor, and pressure is 1～8MPa, is heated to relax 300 ℃～500 ℃ of thermal transition temperatures, keeps t under this temperature _iMin reduces to normal temperature with temperature of reactor then, dismounting reactor and with dilution with toluene reaction product wherein, and extracting after filtration can obtain the productive rate of toluene insolubles (TI), when this productive rate is 0.1wt%, the respective reaction time t of raw material residual oil _iBe exactly thermal response green coke t inductive phase ₀Wherein residual oil raw material is the residue oil after distilling out petrol and diesel oil cut even vacuum distillate or the rich carbon residue or the residue obtained oil of secondary reaction that obtain through solvent deasphalting technology, also can be heavy crude or overweight matter crude oil or coal tar, also can be the mixture of two or more above-mentioned raw materials;

(2) residual oil raw material is mixed with narrow fraction oil, blending ratio by weight is 1: 0.01～1: 5, with aforementioned thermal response green coke t inductive phase that is in residual oil raw material under the mixing condition that measures with quadrat method ₁Wherein narrow fraction oil is solar oil, heavy gas oil, light wax oil or the wax slop from the coking product liquid, perhaps from hydrogenated oil, virgin petroleum fractions, reformed oil, fluid catalytic cracking decant oil, ethylene bottom oil or coal tar, with one or more mixture of above-mentioned narrow fraction oil as the recycle stream of raw material;

(3) with residual oil raw material and thermal response green coke t inductive phase that measures residual oil raw material ₁The time respective cycle logistics mix by internal circulating load, blending ratio by weight is 1: 0.01～1: 5, mixture pump delivered to be heated in the coking heater pipe enter into coke drum behind 485～505 ℃ of the coking temperatures and carry out delayed coking reaction, the oil gas product enters the coking fractional distillation column separation and obtains clean or white, and coke produced then is flocked in the coke drum.

2. according to the described improved method of delay coking process of claim 1, it is characterized in that containing in the recycle stream active ingredient that a certain amount of promotion hydrogen atom discharges, this active ingredient is to have the partial hydrogenation aromatic hydrocarbons that is similar to the naphthane chemical structure.

3. according to the described improved method of delay coking process of claim 1, it is characterized in that the internal circulating load of recycle stream accounts for the 1wt%～100wt% of residual oil raw material.

4. according to the described improved method of delay coking process of claim 1, it is characterized in that the internal circulating load of recycle stream accounts for the 5wt%～50wt% of residual oil raw material.

5. according to the described improved method of delay coking process of claim 1, it is characterized in that to inject when compound advances delayed coking unit the high-temperature vapor of the 0.5wt%～3.0wt% that accounts for the residual oil amount.